1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording material.
2. Related Background Art
There are already proposed various digital copying apparatus for reading an original image with an image sensor such as CCD and reproducing said original image on a recording material such as paper, based on the output of said image sensor. Such digital copying apparatuses are easily capable of electrically enlarging the original image with an arbitrary image magnification factor and the present applicant already proposed, in the Japanese patent application Sho No. 62-289182, to record the original image in a size larger than that of the recording material, by dividing the image of a page, by enlarging thus divided images and by recording said images on plural recording sheets.
For example, the copying of an original of A4 size (210.times.297 mm) with an enlargement ratio of 600% will result in a print of 1260.times.1782 mm as shown in FIGS. 1A and 1B, wherein FIG. 1A indicates the A4-sized original in laterally oblong position, and FIG. 1B indicates the print with an enlargement ratio of 600%. If the rolled print sheet has a width corresponding to the longer side of A2 size (594 mm), the A4-sized original is divided into three portions (1), (2) and (3) as shown in FIG. 1A, and these portions are respectively copied on print sheets (1'), (2') and (3') as shown in FIG. 1B.
If cut sheets, for example of A3 size, are used in such enlarged printing, there will be required 18 sheets in the above-mentioned example, involving a considerable amount of pasting work for obtaining a single print. On the other hand, the use of a rolled sheet as shown in FIGS. 1A and 1B with an arbitrary amount of sub scanning allows to reduce the number of sheets required and to obtain a larger copy.
However such large-sized copying with rolled sheet requires a very long copying time. Such large-sized copying, if once started, occupies the image forming apparatus (copying machine), excluding other small-sized copying needed urgently. Also if the copying operation is interrupted when the operator has to urgently leave the apparatus or due to the power interruption, the printing operation has to be restarted from the beginning. Also, since such large-sized copying consumes a large amount of rolled sheet, the copying operation may be interrupted if the sheet runs out during the copying operation.
In a conventional printer utilizing a rolled sheet, the rolled sheet 703 bears, as shown in FIG. 2, a striped mark 701 of different reflectivity for example along a lateral edge close to the end portion, and the limited remaining amount of the rolled sheet 703 is identified by detecting said mark 703 with a photosensor 702. When the limited remaining amount of the recording sheet is detected, a corresponding display is made on the display unit of the printer, and the next recording operation is prohibited until the recording sheet is loaded anew.
However, such striped mark for detecting the end of the recording sheet will deteriorate the quality of the recorded image, since said mark remains along the recorded image in the end portion of the sheet. Also after the display of absence of the recording sheet in response to the detection of limited remaining amount thereof, the replacement of the recording sheet is usually identified by the opening/closing of a door of a reservoir housing such recording sheet. However, even if the recording sheet of a small amount is loaded by opening and closing said door, the display for absence of recording sheet is cancelled though the actual amount of the recording sheet is small.